Fish farming (aquaculture) is increasingly supplying protein for humans, but its effect on freshwater environments is not well understood. At one IISD-ELA lake, researchers installed an aquaculture cage and stocked it with a high density of rainbow trout and monitored changes of the lake ecosystem. They found significant increases in nutrient delivery to the water and sediments of the lake, and consequently, detectable increases in algae growth in the water. These results suggest that freshwater fish farms can negatively impact lake water quality, and they highlight the need to develop aquaculture legislation focused on reducing the environmental effects of its operations.